Circuit array for setting the operating point of a transistor

ABSTRACT

In a circuit array for setting the operating point of a first transistor. A current-inverting circuit (current mirror circuit) has a pinch resistor connected in series with the base-emitter path of another transistor within the current inverting circuit. The current inverting circuit supplies the current-inverting base current of the first transistor.

BACKGROUND OF THE INVENTION

The invention is concerned with setting the operating point oftransistors, in particular bipolar transistors, in an integrated circuitin which the collector currents of the transistors are predetermined bythe base-emitter currents. These base-emitter currents can be fixed byresistors, for example, via which the base-emitter paths are fed by asupply voltage. Setting of the operating point in this way has theadvantage that relatively low operating voltages are possible with aminimum of operating current. The low operating voltage possible is aresult of the fact that the emitter potentials, e.g. of npn transistors,can be directly connected to the negative terminal of the supplyvoltage. The minimum operating current is possible because only thebase-emitter currents are required in addition to the collector currentsneeded for the circuit to function. The drawbacks of setting theoperating point in this way are that with predetermined resistances foroperating point setting, the collector currents depend on the currentamplification factors of the transistors and on the base-emittervoltages that are obtained.

In general, negative-feedback arrays are used for operating pointsetting of transistors, such as negative emitter feedback, where anemitter-current-stabilizing resistor is provided and where the base issupplied with a fixed potential.

SUMMARY OF THE INVENTION

The object of the invention is to provide a circuit array for settingthe operating point in a transistor that offers the possibility of thetransistor electrodes accepting different potentials, thereby achievinga degree of freedom for dimensioning the stage in which the transistoris used. According to the invention, there is provided a circuit arrayfor stabilizing the operation of a transistor, wherein acurrent-inverting, i.e., current-mirror, circuit is provided thatsupplies the base current of the transistor.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail, by way ofexamples, with reference to the drawings, in which

FIG. 1 shows a circuit array, according to the invention, for settingthe operating point of a transistor,

FIG. 2 shows a pinch resistor,

FIG. 3 shows a circuit array with a current-inverting or current-mirrorcircuit that sets the operating point of two transistors,

FIG. 4 shows a section of the circuit in FIG. 3,

FIG. 5 shows also a section of the circuit in FIG. 3,

FIG. 6 shows a circuit array for setting the operating point having acurrent-inverting circuit comprising three transistors,

FIG. 7a shows a circuit in which the current to be inverted for thecurrent-inverting circuit originates from the collector of a transistor,

FIG. 7b shows part of the circuit in FIG. 7a,

FIG. 8 shows a circuit similar to FIG. 7a,

FIG. 9 shows a further embodiment of the circuit in accordance with theinvention,

FIG. 10 shows a circuit in which current-inverting circuits arecontrolled by a current-inverting circuit,

FIGS. 11 to 14 show circuits controlling the collector currents of npntransistors.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a circuit array in accordance with the invention, where acurrent-inverting or current-mirror circuit comprising transistor 1supplies, together with resistor 2, the base-emitter currents forsetting the collector current of transistor 3.

The current-inverting (current-mirror) circuit converts the currentflowing in resistor 2 at a certain ratio (inversion ratio) to thecollector current of the collector of transistor 1. The respectivecurrent inversion ratio is determined here by the design of theinverting transistor 1. In the embodiment in FIG. 1, the invertingtransistor 1 is a lateral pnp transistor with several collectorsegments. The size of the current flowing through resistor 2 isdetermined by the supply voltage from source 4, the base-emitter voltageof transistor 1, and the value of resistor 2. By contrast, the currentamplification factor of transistor 1 has a relatively minor effect onthe current inversion ratio. A substantial feature of the circuit inFIG. 1 according to the invention (and also of the other circuits) isthe type of resistor 2. This resistor is a so-called pinch resistorwhich is made together with transistor 3. A pinch resistor comprises,according to FIG. 2, a resistance zone 5 limited in the verticaldirection by two semiconductor zones 6 and 7. Semiconductor zones 6 and7 are of the opposite conductivity type to resistance zone 5. Resistancezone 5 is made in the same process step as the base zone 8 of thetransistor 3 situated next to the pinch resistor in FIG. 2, so thatresistance zone 5 has the same conductivity type, the same conductivityand the same penetration depth as the base zone 8 of transistor 3. Insimilar manner, the semiconductor zone 6 located above the resistancezone 5 and bordering the semiconductor surface is made in the sameoperation as emitter zone 9 of transistor 3, so that semiconductor zone6 has the same conduction, the same conductivity and the same depth asemitter zone 9 of transistor 3. The semiconductor element of theintegrated circuit array in FIG. 2 comprises a substrate 10 of the firstconductivity type and an epitaxial layer 11 of the second conductivitytype. The electrical separation of the circuit array components in FIG.2 is achieved with separation zones 12 of the first conductivity type.Resistance zone 5 and base zone 8 are of the first conductivity type.Concealed layers 13 and 14 of the second conductivity type areunderneath pinch resistor 2 and transistor 3.

Using a pinch resistor has the advantage that its resistance valuecorrelates with the current amplification factor (H_(FE)) of theintegrated (npn) transistor 3 in such a way that the resistance value ofpinch resistor 2 is substantially proportional to the currentamplification factor of the (npn) transistor 3. Under thesecircumstances, it is possible in the circuit according to the inventionto compensate for the effect caused by the current amplification factor(H_(FE)) dispersion on the collector current of transistor 3 by theopposite-acting dispersion of pinch resistor 2.

A further substantial feature of the invention is the dimensioning ofthe supply voltage from source 4. The value of this supply voltage hasan effect on the temperature development of the set collector current.There is an optimum value for the supply voltage from source 4 for thecollector current of transistor 3 to be largely dependent ontemperature. This is based on the fact that the temperature developmentof pinch resistor 2 is strongly positive and that the temperaturedevelopment of the base-emitter voltage of transistors, and so oftransistor 3, is negative (approx. -2 mV/K), as is well known. It istherefore possible to compensate not only the temperature development ofthe collector current, but also to set both a positive and a negativetemperature development for the collector current of transistor 3.

As can be seen from FIG. 1, it is not necessary to set the emitterpotential of transistor 3 to reference potential, since the base-emittercurrent supply to transistor 3 in accordance with the invention islargely independent of the emitter potential of transistor 3, providedthe circuit-inverting transistor 1 is not set to saturation.

The circuit array in FIG. 3 differs from that in FIG. 1 in that thecurrent-inverting circuit not only sets the operating point of atransistor 3, but also the operating points of two transistors (3, 15)by the base-emitter currents of transistors 3 and 15 for setting thecollector currents of transistors 3 and 15 being generated bycurrent-inverting circuit 1 and pinch resistor 2. The current-invertingcircuit (1) converts the current flowing in pinch resistor 2 at acertain ratio (inversion ratio) to the collector currents of transistors3 and 15. The respective current-inverting ratio is determined by thedesign of the current-inverting transistor 1. The current-invertingtransistor 1 is, as in the embodiment in FIG, 1, a lateral pnptransistor with several collector segments. By using a pinch resistor 2it is possible with the circuit array in FIG. 3 to insert a resistor 16,for example, into the emitter line of transistor 15, withoutsubstantially affecting the collector current in transistor 15. Theinvention therefore gives a relatively high degree of freedom whendimensioning the circuit components. In the circuit array according toFIG. 3, resistor 17 is in the collector line of transistor 3 andresistor 18 in the collector line of transistor 15. The circuit array inFIG. 3 has a second voltage source 19 whose voltage is greater than thatfrom source 4. One terminal of voltage source 19 is connected to theemitter of transistor 15 via resistor 16 and to the emitter ofcurrent-inverting transistor 1 via pinch resistor 2. The second terminalof voltage source 19 is connected to the collector of transistor 15 viaresistor 18.

The FIG. 3 circuit shows in a dashed line a modification in the form ofa further pinch resistor 2'. The use of this resistor 2' permits the useof a higher value for the supply voltage from source 4, with the samesettable temperature development for the collector currents oftransistors 3 and 15. Resistor 2' forms with resistor 2 a voltagedivider that diverts the voltage value necessary for temperaturedevelopment compensation by voltage division from the supply voltage(4). In order to make the size of the collector currents set accordingto the invention independent of changes in the operating voltage,appropriate stabilization of the supply voltage (4) normally divertedfrom the operating voltage is necessary.

FIG. 4 shows a section (current-inverting or current-mirror transistor,pinch resistor) of the circuit according to FIG. 3. In contrast to thecircuit in FIG. 3, the circuit section shown in FIG. 4 has a furthertransistor 20 whose collector-emitter path is connected in series toresistor 2. This transistor 20 serves as a switch for turning thecurrent-inverting circuit on and off. Switch-on is achieved byimprinting a current into the base of transistor 20. The necessary sizeof this current can for example be up to 10 times smaller than thecurrent to be generated in resistor 2. This makes it possible to switchall collector currents set with the circuit on and off using arelatively low switching current (standby function).

FIG. 5 shows a further section through the circuit according to FIG. 3,where instead of a lateral pnp transistor with several collectorsegments several pnp transistors (1', 1", 1'") can be used.

FIG. 6 shows a circuit according to the invention in which thecurrent-inverting circuit is built up of transistors 1, 21 and 22. Thisarray has the advantage over previously shown current-inverting arraysthat the current inversion ratio is more independent of the currentamplification factors of the pnp transistors used. The base-emittercurrents for setting the operating point in accordance with theinvention of the (not shown) transistors are taken from the collectorsof the circuit-inverting transistor 1. In the circuit according to FIG.6 the voltage source 4 requires in comparison with previous circuitsabout double the supply voltage for the same temperature dependence ofthe set collector currents. Instead of the described current-invertingtransistors, other known current inversion arrays can also be used.

FIG. 7a shows a current in accordance with the invention in which thecurrent to be inverted for the current-inverting circuit 1 originatesfrom the collector of transistor 23. The collector current of thistransistor 23 is practically identical to its emitter current, whichresults from the supply voltage from source 4 in conjunction with theseries connection comprising the base-emitter path of transistor 23 andresistor 2. Since the current-inverting array with transistor 1 and itsemitter connection can be based on supply voltage source 24, greaterpotential differences can be achieved for the bases controlled by thecurrent-inverting circuit 1 via collectors 1b and 1c.

FIG. 7b shows a circuit detail of the circuit according to FIG. 7a.Separate pnp transistors 1', 1" and 1'" are used for the currentinversion, with the resistors 25a, 25b and 25c being inserted inaddition into the emitter lines of these transistors.

When the size of the voltage obtained at these resistors is greatenough, negative feedback is obtained which reduces the detrimentalinfluences of the early effect of current-inverting circuits (dependenceof the output currents of the current-inverting transistors on changesin the supply voltage) corresponding to the degree of negative feedback.To achieve an effective negative feedback, correspondingly high valuesfor resistors 25a, 25b and 25c are required on account of the generallylow currents in these transistors. In this connection, it is anadvantage to use pinch resistors here too, as for resistor 2. As is wellknown, this type permits higher resistances to be achieved easily with alow chip surface requirement. Use of this resistor type for resistor 2and for negative feedback resistors 25a, 25b and 25c has at the sametime the effect of making the degree of negative feedback independent ofthe dispersion of these pinch resistors.

The circuit array in FIG. 8 differs from the circuit according to FIG.7a in that the collector connection 1a of current-inverting transistor 1is not connected to the base of the same transistor (1), but to theemitter of transistor 23. The advantage of this circuit is that theinfluence of the early effect on the output currents (1b, 1c), based onthe change in the supply voltage from source 24, is reduced. This isachieved by the control loop formed by the feedback of part of thecollector current from transistor 1 to the emitter of transistor 23.This control loop has the effect that changes in the collector currentin collector 1a caused by the early effect are largely eliminated byadjustment. The changes in the output currents in collectors 1b and 1care also thereby reduced (regulated).

FIG. 9 shows an embodiment of the invention. In the array according toFIG. 9 the base-emitter path of transistor 23 is connected in parallelwith the base-emitter path of a further transmitter 25 whose emittersurface is, as indicated in FIG. 9, for example twice the size of theemitter surface of transistor 23. The collectors of transistors 23 and25 are connected to the symbolically indicated current-inverting arrays26 and 27 respectively. These current-inverting arrays supply at theiroutputs (26a, 26b, and 27a, 27b and 27c) the base-emitter currents forsetting the collector currents of npn transistors (not shown). Theobject of this circuit is to distribute the currents passing to thecurrent-inverting circuits 26 and 27 in accordance with the surfaceratio of the emitter surfaces of transistors 23 and 25. In the examplein question, 1/3 of the current generated in pinch resistor 2 passes tocurrent-inverting circuit 26, and 2/3 to current-inverting circuit 27.

FIG. 10 shows a circuit in accordance with the invention wherebycurrent-inverting (current-mirror) circuits 26 and 27 are controlled bya current-inverting circuit comprising transistors 28, 29 and 30. Thecurrent controlling this current-inverting circuit is determined bypinch resistance 2 in conjunction with the supply voltage of source 4.

The circuits according to the invention and described in FIGS. 11, 12,13 and 14 are based on the control of collector currents of npntransistors. The control of collector currents is used for controllingthe amplification of transistor stages, for example. For this purpose,the base-emitter currents of the transistors to be controlled are, inaccordance with the invention, changed by a control signal. It isnecessary or advisable here, for special applications, thatreverse-direction control of collector currents is provided.Furthermore, it may be necessary in the case of reverse-directioncontrol of collector currents to design it so that the sum of thesecontrolled currents remains constant.

FIG. 11 shows a circuit array in accordance with the invention forreverse-direction control of two npn transistors (not shown). In thiscircuit two current-inverting arrays 31 and 32 are controlled by thecollectors of transistors 33 and 34. The output currents with which thenpn transistors are controlled are taken from collector 31b and 32b. Theoutput currents are controlled by the control of the emitter currentdistribution of transistors 33 and 34 by the change in the basepotential of transistor 34, e.g. by means of the variable voltage ofsource 35.

An embodiment of the circuit according to FIG. 11 is shown in FIG. 12a.In this circuit transistor 36 forms together with current-invertingarray 37 a DC control circuit via the connection of collector 37a to theemitter of transistor 36. This control loop has the effect of keepingthe sum of the base current for current-inverting transistor 37 and ofthe collector current of collector 37a constant. The sum of thesecurrents is equal to the current flowing through pinch resistor 2. Here,the base current of transistor 36 is negligible. The collector currentof collector 37b has a certain ratio to the collector current ofcollector 37a and passes to the common emitter connection of transistors33' and 34'. By controlling the base potential of transistor 34' thiscurrent is divided between the two collectors 33a and 34a. With thedescribed DC circuit the influence of the early affect ofcurrent-inverting transistor 37 on the output currents (33a and 34a),based on the voltage change of supply voltage source 4, is reduced.Compared with the circuit according to FIG. 11, this circuit achieves ahigher constancy in the sum of the controlled collector currents.

FIG. 12b shows an embodiment of the circuit according to FIG. 12a.Compared with the circuit according to FIG. 12a, an additionaltransistor 38 is provided to whose emitter the current of collector 37ais passed. The collector current (38a) of transistor 38 is passed to theemitter of transistor 36. The advantage of this circuit type over thecircuit according to FIG. 12a is that the potentials of collectors 37aand 37b are identical, thereby further reducing the influence of theearly effect. In addition, the influence of the current amplificationfactor of transistors 33' and 34' on the output currents of collectors33a and 34a is compensated by the reverse-direction influence of thecurrent amplification factor of transistor 38 in the circuit accordingto FIG. 12b.

FIG. 13a shows a circuit in accordance with the invention in which thecurrent control (current distribution) is effected via transistors 33and 34, as for FIG. 11. However, the difference to FIG. 11 is that thecurrent to the emitters of transistors 33 and 34 does not pass via aresistor, but via a current-inverting circuit with transistors 39 and40. The current generated in this current-inverting circuit isdetermined with pinch resistor 2. To reduce the influence of the earlyeffect of current-inverting transistors 31 and 32, collectors 31a and32a are connected to the emitters of transistors 33 and 34. Unlike inthe circuit according to FIG. 11, this achieves both a reduction in theinfluence of the early effect and a higher constancy in the sum ofcontrolled collector currents (31b and 32b).

FIG. 13b shows an addition to the circuit in FIG. 13a, whereby thecollector-emitter path of a transistor 41 is inserted into the supplyline from the supply voltage source 1 to the connection point ofresistor 2 and the base of transistor 33. This transistor 41 acts as aswitching transistor with which the circuit can be switched on and offwith base control 41a. Both a pnp transistor, as shown in FIG. 13b, andan npn transistor can be used as the switching transistor 41. To switchon the circuit the transistor 41 must be controlled by a correspondinglyaligned base current in the flow direction.

FIG. 14 shows a circuit in accordance with the invention for use in acontrolled-amplification receiver pre-stage. In the circuit according toFIG. 14, transistor 42 is used as the amplifier transistor in the mainbase circuit, where the signal passes to the emitter of transistor 42and the amplified signal is picked up by collector circuit 43. Theamplified signal passes to a following mixer stage, for example. Tocontrol the signal amplification, the base-emitter DC current oftransistor 42 is, in this circuit array, controlled via the collector31b of the current-inverting transistor 31. The transistor 44, connectedas a diode, has the job of diverting the input signal current to thereference potential via capacitor 45 during downward control of theamplification. For this purpose transistor 44 is set conductive via theemitter direct current of transistor 46. The base current for transistor46 is supplied by collector 32b of the current-inverting transistor 32.

Control of current distribution for transistors 42 and 46 is achievedvia the base potential of transistor 34. Control signal 47 is suppliedby a control signal source (not shown), for example. Control follows theprinciple of the circuit shown in FIG. 11. Accordingly, the collectorcurrents of transistors 42 and 46 are controlled with reverse direction,with the sum of controlled collector currents remaining almost constant.This ensures, for example, that the load from current supply source 4undergoes practically no change during control of amplification. At theinput of the circuit is a coil 48 which achieves a DC connection to thereference potential. The capacitor 49 has the same function as capacitor45. Capacitor 50 separates the potential of the collector of transistor42 from the following part of the circuit (mixer stage).

What is claimed is:
 1. In an integrated circuit including a firsttransistor and circuit means for setting the operating point of saidfirst transistor, with said circuit means including current-inverting(current mirror) means having at least one current inverting transistorconnected to receive an input current and to provide the base current ofsaid first transistor, the improvement comprising:a pinch resistorconnected in series with the base-emitter path of said at least onecurrent inverting transistor and determining said input current; whereinthe series connection of said pinch resistor and said base-emitter pathof said at least one current-inverting transistor is connected across afirst voltage source; and wherein the voltage of said voltage sourcedetermines the temperature development of said first transistor.
 2. Acircuit according to claim 1, wherein said at least one currentinverting transistor is a multi-collector transistor having onecollector connected to provide an output current for said base of saidfirst transistor and a further collector connected to one end of saidpinch resistor.
 3. A circuit according to claim 1, wherein saidcurrent-inverting circuit means includes at least two current-invertingtransistors, the collector of one of said at least two current-invertingtransistors being connected to one end of said pinch resistor, and thecollector of the other of said at least two current-invertingtransistors being connected to provide an output current for the base ofsaid first transistor.
 4. In an integrated circuit including a firsttransistor and circuit means for setting the operating point of saidfirst transistor, with said circuit means including current-inverting(current mirror) means having at least one current inverting transistorconnected to receive an input current and to provide the base current ofsaid first transistor, the improvement comprising:a pinch resistorconnected in series with the base-emitter path of said at least onecurrent inverting transistor and determining said input current; whereinthe series connection of said pinch resistor and said base-emitter pathof said at least one current-inverting transistor is connected across afirst voltage source; wherein a second transistor is provided forcontrolling said current-inverting circuit means, said second transistorhaving its collector-emitter path connected between said pinch resistorand the base of said current inverting transistor; wherein a firstterminal of a second voltage source is connected to the base of saidsecond transistor; and wherein a second terminal of said second voltagesource is connected to one terminal of the first voltage source.
 5. Acircuit according to claim 4, wherein said second voltage sourcesupplies a lower voltage than said first voltage source.
 6. A circuitaccording to claim 4,wherein said circuit includes a plurality of saidfirst transistors whose operating points are to be controlled; whereinsaid current-inverting circuit means includes a plurality of saidcurrent inverting transistors each having its base-emitter pathconnected in series with said pinch resistor; wherein each of saidplurality of first transistors has its base connected to receive anoutput of a respective one of said plurality of current invertingtransistors; and wherein means are provided to reduce the effect ofvoltage changes in said first voltage source on the output of saidcurrent inverting transistors of said current-inventing circuit means.7. A circuit according to claim 6,wherein said means to reduce theeffect of voltage changes in said first voltage source on the outputs ofsaid current inverting transistors of said current-inverting circuitmeans comprise respective emitter resistors provided in respectiveemitter supply lines of said current inverting transistors.
 8. A circuitaccording to claim 7, wherein said emitter resistors are pinchresistors.
 9. A circuit according to claim 4, wherein saidcurrent-inverting transistor is a multi-collector transistor whichprovides an output current at one collector;wherein a further transistoris provided whose emitter is connected to a further collector of saidmulti-collector current-inverting transistors; wherein the collector ofsaid further transistor is connected to one end of said pinch resistor;and wherein the base of said further transistor is connected to the baseof said second transistor controlling said multi-collectorcurrent-inverting transistor.
 10. A circuit according to claim 4,wherein said current-inverting circuit means includes at least two ofsaid current-inverting transistors having their respective basesconnected together;wherein a further transistor is provided whoseemitter is connected to the collector of one of said current-invertingtransistors; wherein the collector of the other of said currentinverting transistors provides an output current from said currentinverting circuit means; wherein the collector of said furthertransistor is connected to one end of said pinch resistor; and whereinthe base of said further transistor is connected to the base of saidsecond transistor controlling said one of said current-invertingtransistor whose collector is connected to said emitter of said furthertransistor.
 11. A circuit according to claim 6 wherein a further of saidcurrent-inverting transistors has its collector connected to a commonconnection of its base and the collector of said second transistor. 12.In an integrated circuit including a first transistor and circuit meansfor setting the operating point of said first transistor, with saidcircuit means including current-inverting (current mirror) means havingat least one current inverting transistor connected to receive an inputcurrent and to provide the base current of said first transistor, theimprovement comprising:a pinch resistor connected in series with thebase-emitter path of said at least one current inverting transistor anddetermining said input current; wherein the series connection of saidpinch resistor and said base-emitter path of said at least onecurrent-inverting transistor is connected across a first voltage source;wherein a second transistor is provided for controlling saidcurrent-inverting circuit means, said second transistor having itscollector-emitter path connected between said pinch resistor and thebase of said current inverting transistor; wherein a second voltagesource terminal is connected to the base of said second transistor;wherein several of said current-inverting circuit means and several ofsaid second transistors, each connected to said pinch resistor, areprovided; and wherein each of said current-inverting circuit means iscontrolled independently by a respective one of said second transistors.13. A circuit according to claim 12, wherein the emitters of said secondtransistors controlling the respective current-inverting circuit meansare connected to one another.
 14. A circuit according to claim 13,wherein the bases of second transistors controlling the respective saidcurrent-inverting circuit means are connected to one another.
 15. Acircuit according to claim 14, wherein the respective said secondtransistors controlling the respective current-inverting circuit meanshave different emitter surfaces.
 16. A circuit according to claim 15,wherein the currents for the respective said current-inverting circuitmeans are determined by said emitter surfaces of the respective secondtransistors.
 17. A circuit according to claim 12, wherein the respectivesecond transistors control the current passing to the respectivecurrent-inverting transistors of the respective current-invertingcircuit means.
 18. A circuit according to claim 17, wherein the emittersof said second transistors controlling the respective current-invertingtransistors are connected to one another, and to said pinch resistors;andwherein the control currents for the respective current-invertingtransistors are controlled by the base potentials of the respectivelyassociated second transistors.
 19. A circuit according to claim 13,wherein the bases of said second transistors controlling the respectivecurrent-inverting circuit means are connected to one another.
 20. In anintegrated circuit including a first transistor and circuit means forsetting the operating point of said first transistor, with said curcuitmeans including current-inverting (current mirror) means having at leastone current inverting transistor connected to receive an input currentand whose output provides the base current of said first transistor, theimprovement comprising:a pinch resistor connected in series with thebase-emitter path of said at least one current inverting transistor anddetermining said input current; wherein a plurality of said firsttransistors are provided whose operating points are to be set; andwherein the operating points of said first transistors are set by saidcurrent-inverting circuit means.
 21. A circuit according to claim 20,further comprising means for controlling base-emitter currents of onesof said first transistors whose operating points are set differently.22. A circuit according to claim 20, further comprising a differentialamplifier connected to divide said current-inverting transistor outputinto two currents for ones of said first transistors whose operatingpoints are differently set.
 23. In an integrated circuit including afirst transistor and circuit means for setting the operating point ofsaid first transistor, with said circuit means includingcurrent-inverting (current mirror) means having at least one currentinverting transistor connected to receive an input current and whoseoutput provides the base current of said first transistor, theimprovement comprises:a pinch resistor connected in series with thebase-emitter path of said at least one current inverting transistor anddetermining said input current; wherein a circuit means, including afurther transistor, is provided for interrupting said series connectionof said pinch resistor and said at least one current invertingtransistor.
 24. In an integrated circuit including a first transistorand circuit means for setting the operating point of said firsttransistor, with said circuit means including current-inverting (currentmirror) means having at least one current inverting transistor connectedto receive an input current and whose output provides the base currentof said first transistor, the improvement comprising:a pinch resistorconnected in series with the base-emitter path of said at least onecurrent inverting transistor and determining said input current; whereinsaid first transistor whose operating point is set included in anamplifier circuit; wherein two of said first transistors are used insaid amplifier circuit; wherein said current-inverting circuit meansincludes two of said current inverting transistors for providingrespective base currents for respective first transistors; and whereinmeans are provided for controlling the currents of the respective firsttransistors with reverse directions.
 25. A circuit according to claim24, wherein said means for controlling the currents of said firsttransistors with reverse-directions includes means for causing the sumof the base currents of said first transistors to be kept constant. 26.A circuit according to claim 24,wherein said means for controlling thecurrents of said first transistors with reverse-directions includes afurther transistor having a collector-emitter path connected in serieswith said series connection of said pinch resistor and said base-emitterpath of said at least one current inverting transistors, and having abase connected to a control terminal.